1. Field of the Invention
The present invention relates to an inkjet printing apparatus and an inkjet printing method. In particular, the present invention relates to an ejection failure complementary printing method for detecting a printing element where an ejection failure has occurred, and for employing another printing element to complement data to be printed by the defective ejection printing element.
2. Description of the Related Art
An inkjet printing apparatus employs a print head that includes multiple nozzles for the ejection of ink droplets, and during printing, there is a possibility that an ejection failure could suddenly occur at these nozzles, without warning, and cause a printed image to be disfigured by striping and/or variations in printing ink densities. In the event, the main cause of such an ejection failure is the presence of a foreign substance near the nozzles, or the entry of bubbles into the nozzles, and in most cases, such an ejection failure can be corrected for by performing a print head maintenance process. However, in a case wherein continuous paper is being employed for printing, or wherein cut sheet paper is being employed to perform sequential printing, maintaining of a high-speed output capability is important, and therefore, during printing, it is impractical for a maintenance process, which requires a comparatively great deal of time, to be performed frequently.
In such a case, when a so-called ejection failure complement process can be employed, during which printing is performed while print data to be printed by a nozzle whereat an ejection failure has occurred is complemented by using another nozzle, an obstacle, such as stripes and/or density unevenness, does not appear in a printed image, even without a maintenance process being performed. Further, the ejection failure complement process is also effective for an ejection failure that is caused by a heater breakdown or the clogging of nozzles that can not be corrected for by performing the normal maintenance process.
In Japanese Patent Laid-Open No. 2012-71568, an inkjet printing method is disclosed that can perform both a first ejection failure complement process with a comparatively high accuracy, for detecting and correcting the ejection state before the printing operation is performed, and a second ejection failure complement process with a comparatively high processing speed, for detecting and correcting the ejection state during the printing operation. When the ejection failure complement process is prepared in two stages, both a commonly occurring ejection failure and a sudden ejection failure can be appropriately coped with, and an image without stripes and uneven densities can be stably output.
During the ejection failure complement process, information for a nozzle that has been detected as being an ejection failed nozzle is stored in a specific storage unit, and, based on the information, print data for the ejection failed nozzle is allocated for other normal nozzles. Therefore, when printing is performed for an extended period of time while the second ejection failure complement process is being employed, there is a case wherein the number of nozzles that are found to have had an ejection failure has increased more and more, and the printing performed for the nozzles identified as having had an ejection failure can not be complemented by employing normally available nozzles. Further, since the ejection frequencies of the remaining normal nozzles are increased continuously, the service lives of these nozzles may be reduced. Meanwhile, in a case wherein there is a sudden ejection failure, what often happens is that the failed nozzle recovers naturally, during the printing operation, without the maintenance process being performed, and in such a case, when the determination results for the ejection failed nozzle are not updated for a long time, the possibility that the nozzle rejoins the others as a normal nozzle will be lost. Therefore, it is desirable that information for a nozzle that is detected as an ejection failed nozzle be reset at an appropriate timing.
However, in the ejection failure complement process described in Japanese Patent Laid-Open No. 2012-71568, ejection failure information detected both in the first ejection failure complement process and ejection failure information detected in the second ejection failure complement process are stored together, and the total of the two sets of information are employed for the process. Therefore, when information for an ejection failure that suddenly occurred during the printing operation is reset, information for the usual ejection failure that is identified before the printing operation is also cleared, and an image obstacle, such as stripes or density unevenness's, would appear in an image that is printed immediately after the resetting of information has been performed.